Anatomy and Function of the Ear

The Structure Of The Ear

• The outer, middle, and inner ear structures are described.
• The role of the vestibular apparatus is discussed in detecting movement and angular rotation.
• The structure and function of the cochlea and the organ of Corti is explained in relation to hearing.

The Ear

• Mammals have two sense organs in the ear for hearing and balance.
• The ear is divided into the outer, middle, and inner ear.

Outer Ear

• The outer ear includes the pinna, which collects and amplifies sound, and the auditory canal.
• The tympanic membrane, or ear drum, blocks the ear canal.
• The ear drum converts soundwaves into physical vibrations with membrane movement.
• The ear drum can rupture from trauma, leading to hearing loss. Small perforations can heal spontaneously.

Middle Ear

• This consists of the tympanic cavity between the eardrum and the oval window of the inner ear.
• It contains three small bones called the ossicles.
• The Latin names for these bones are malleus, incus, and stapes, which translate to "the hammer, anvil, and stirrup".
• The stapes is the smallest bone in the human body.
• The middle ear bones amplify and transmit vibrations from the tympanic membrane to the inner ear.
• They translate the low-pressure movement of the large eardrum into high-pressure movement of the small oval window.
• The malleus connects to the eardrum, and the incus bone connects to the other side.
• Vibrational energy transfers from the eardrum to the incus.
• The incus transfers energy to the stapes, which connects to the oval window of the inner ear.
• The middle ear also contains the Eustachian tube, which links the back of the nose to the middle ear.
• The Eustachian tube equalizes the pressure between the middle ear and external atmosphere.
• Also helps drain mucous from the middle ear.

Inner Ear

• Innermost section of the ear where physical vibrations of sound waves convert to nerve signals.
• Inner Ear is contained within a hollow cavity in the temporal bone of the skull called the bony labyrinth.
• The membranous labyrinth is a system of fluid-filled chambers and channels found within the bony labyrinth.
• These two structures are separated by a layer of perilymph fluid.
• The inner ear includes the vestibular system and the cochlea.
• The vestibular system provides balance and spatial awareness.
• The vestibular system consists of semicircular canals which detect rotation, and otolith organs which detect linear acceleration.

Semi-Circular Canals

• There are three semi-circular canals that lie at approximate right angles to each other: lateral, anterior, and posterior.
• Each canal contains a fluid called endolymph and ends with a sac called the osseous ampulla.
• Head movements causes endolymph to flow within the canals.
• Different canals detect movement within three planes.

Ampullae and Crista Ampullaris

• Each ampule contains a crista ampullaris.
• Crista ampullaris translate endolymph flow into nerve signals.
• The crista ampullaris consists of a cluster of hair cells encased within a gelatinous, cupula structure.
• When the head turns, endolymph within the semi-circular canals pushes the cupula in the opposite direction of the head.
• This movement triggers membrane depolarization of hair cells.
• Vestibular systems in both ears work together, this allows the body to sense all movement directions.
• Excessive triggering of this system results in motion sickness.

Otolith Organs

• The inner ear includes two otolith organs: the utricle and the smaller saccule.
• The utricle and saccule are filled with endolymph and detect linear acceleration.
• The utricle responds to horizontal movement, and the saccule detects vertical acceleration.
• Both organs contain a sensitive hair cell patch called the macula, which is enclosed within an otolithic membrane.
• Calcium carbonate crystals, or otoliths, cover the top of this membrane.
• Head tilting allows gravity to pull the otoliths forward.
• The process triggers hair cell activation.

Cochlea - Hearing

• The organ of hearing is a coiled tube that resembles a snail shell with three canals separated by thin membranes.
• The upper canal, the scala vestibuli (vestibular canal), connects to the oval window and thus the stapes.
• The lower canal, the scala tympani (tympanic canal) connects to the round window which opens on the middle ear.
• At cochlear apex, the helicotrema connects the scala tympani to the scala vestibuli.

Scala Media

• The scala media separates from the scala vestibuli by a thin vestibular or Reissner's membrane.
• The scala media is separated from the scala tympani by thicker basilar membrane, which does impede sound.
• About 20,000 reed-like thin spines, called basilar fibers, protrude most of the basilar membrane distance.
• The organ of Corti is on scala media basilar membrane , this is the organ of hearing.

Organ of Corti

• The organ of Corti is on the basilar membrane in the scala media.
• The organ of Corti has one row of internal hair cells (3,500) and three to four rows of external hair cells (20,000).
• Cochlear nerve endings enmesh bases and sides of the hair cells.
• This network leads to of the spiral ganglion of Corti in the core of the cochlea.
• Axons from the spiral ganglion travel through the cochlear nerve to the brain, via the VIII auditory nerve.
• Minute hairs or stereocilia project from each hair cell.
• Stereocilia either touch or embed in the surface gel of the tectorial membrane overhanging flap of tissue.
• The tectorial membrane lies free in the scala media, attached on one side.
• Stereocilia arrange with the shortest hairs on the outer rows and the longest in the center.
• Sound vibrations from the oval window are transmitted by the stapes, creating pressure waves in the scala vestibuli and scala media.
• Causes the basilar membrane vibrates which move the hair cells against the tectorial membrane.
• Bending stereocilia causes ion channels to open, this allows potassium and calcium to enter the cell.
• This triggers release of glutamate neurotransmitter with subsequent activation of postsynaptic cochlear nerves
• Also triggers creation of a nerve impulse.

Soundwave Frequency or Pitch

• The basilar membrane composes of 20,000+ basilar fibres from the oval and round windows toward the helicotrema.
• The basilar membrane varies from 0.04mm at the windows to 0.5mm at the apex, giving a distance of 35mm.
• Fibres are fixed at their basal ends but free at the distal end, loosely embedded in the basilar membrane.
• Fibre diameter decreases from base to helicotrema.
• Short, stiff fibres at the windows vibrate at high frequency, and long, thin fibres at the helicotrema vibrate at low frequency.
• Sounds pitch/ frequency is based on the place principle in the activated part of the basilar membrane.

Integument: Epidermis, Dermis

• The role of the skin as a significant organ in the integumentary system is emphasized.
• Epidermis's histology is described, focusing on cell types, layers, and processes like keratinization.
• Various epidermal derivatives and keratinized structures including nails, hair, sweat glands, and mammary glands are discussed.
• The dermis and subcutaneous layers of the skin are described.
• Skin constitutes an integument for the entire body. Plays roles in protection, thermoregulation, sensation, and metabolism.
• Skin protects by its tough hide, pathogens defense, water regulation, and defending against dangerous UV light.
• Skin provides insulation via hair and sweating, playing a major role in temperature regulation.
• Skin origin is from the area of sensory and nervous structures in the ancestral metazoan.
• Skin originates continuity embryologically with the nervous system.
• It produces vitamin D which is used calcium and phosphate metabolism.
• Sensational sensory nerve endings interpret external environment, temperature, and pain.
• Skin equals 12.5% to 16.7% of the mass of a normal person.
• It varies in thickness - very thin eyelids, thick on soles of feet.
• Continuous integument with the digestive tract, mouth, anus, urinary, genitals, penis, vagina, and urethra.
• Composed of two layers - outer epidermis and an inner dermis with a hypodermis, the underlayer of loose connective tissue.
• Glabulous skin: thick, hairless skin. Ex: palms and soles of feet.
• Hairy skin: thinner skin - Most skin areas.

Epidermis Strata and Protection

• Protective barrier that guards against chemical, physical, and microbial factors.
• It is 0.06-0.1 mm thick.
• This arises from embryonic ectoderm and gives rise to sweat glands, sebaceous glands, and mammary glands.
• Keratinocytes arrange into strata, creating stratified, squamous epithelium.
• Keratinocytes start at the basal membrane and move progressively outwards.
• Cells mature to corneocytes and are removed by desquamation, which produces a stratum comeum.
• The entire epidermal cycle takes about 27 days.
• A thick, outer layer of flattened, fused cell remnants made of keratin.
• This is covered with an oily secretion from sebaceous glands (sebum).
• Found only in thick skin; a clear of cells homogenous, and lacks nuclei or organelles.
• Shows internal granules within the cell.
• Prickle layer, where cells grow, showcasing early keratin synthesis.
• This contains a proliferative layer of columnar or cuboidal cells.

Skin 3-Factor Pigmentation

• Carotene creates Yellowish that derives from subcutaneous fat.
• Hemoglobin affects capillary dermal concentration and oxygenation.
• Special branched cells also affect pigment that is scattered throughout the stratum basale.
• Melanin is the cells pigment produce melanocytes.
• Pigment able to dissipate over 99.9% of uv radiation to protect from uv radiation.
• Melanocytes number constant irrespective of skin color.
• Melanosomes are vesicles where melanocytes package melanin.
• Keratinocytes take these into the nucleus to protect the DNA from ionizing radiation.
• A patch of dark pigmentation, for example, a mole, is a melanocytic nevus that produces melanoma in percentage.

Keratinised Structures

• Mammals and foot pads primates, and humans, feature friction ridges on the palms and soles, fingerprint dermatoglyph.
• Hair, Nails, claws, hooves, make most of keratinised structures.
• Hair (shaft), which grow from a root (hair bulb) lying in the dermal layer that forms from epidermal cells.
• Hair bulb are located at a base sunk in a pit, the dermis, called the hair follicle that is made by epidermal cells, thus continuous.
• Epidermis cells grow down into forming a cellular shaft during life.
• Hairshaft or dead epidermal matrix with the growing matrix cell exists.
• The vas plug of dermis that the matrix forms is called the dermal matrix.
• Germinal matrix cells are connected via dermis cellular layer(s).
• The structure makes a pilosebaceous unit.
• Germinal matrix gives hair growth.
• Proliferation starts with cells pushed through the follicle.
• Cells supply become keratinized and die.
• Hair follicle is organized cells that are initial.

Hair Structure

• They perform to create the cortex single and cell single.
• Glands/cell/hairs enter and exit on basis of the cycles from:
• permanent.
• Bulge.
• Exogen.
• Bulb phases grow around hair bulb and the muscle arrector pili with some sebaceous activity.

Hair Follicle Structure

• Hair Follicle is in position the of the hair sheaths with:
• Medulla: seldom seen.
• Cortex: keratin.
• Cuticle single-layer over position on follicles, but needs outer sheath.
• Germination needs external and internal.
• Cells perform the cortex with outer/cuticles.

Hair Growth Cycle - Anagen, Catagen, and Telogen

• Hair grows in cycles, so phases are active, and rest stages are required depending on sebaceous for proper maintenance and regeneration of the hair follicles.
• Hair can be elevated via muscle.
• Glands produce and move.
• Cycle involves bulge to grow hair as well to the matrix or matrix and with cell/glands phases and muscle for elevation.
• Telogen is then entered when old or hair shaft loosens.
• In baldness, the matrix phases don't resume.

Sudoriferous & Sebaceous Glands

• Sweat and Oil Glands are found in Hair Follicles and the Skin
• Types;
• sudoriferous helps with oil with holocrine for oil
  • for skin and hair production
  • the palms of feet and hand
• Most areas of body and the limbs is regulated with skin, oil and glands/unit.
• Ducts open for thermoregulation, and sweat at most areas outside lip and eardrums with fascia connected to the skin.
• Apocrine Ducts also exist in the hair or epidermis through axillary/arm pits (breast).

Ceruminous and Mammary Integument Structure

• Ceram is related to audio structure where is drains external sudatory and also contains secretion with lubricants, bacteria, water protection through sand, wax.
• Mammae are what's called glands of with derivatives for their control such as:
• Composition, protein milk from animals.
• Pig dog cow is similar, but can have lines.

Dermis Properties Description

• Cells in dermis, most fibers secrete and organize fibroblasts called: ECM

• Major, fibrillar, 1, 2,3, v elastin

• Papillary dermis that is Rich in vasculature and can Thermo/ Nerve Endings

• Reticular – dermis contains elastin and provide with structural skin.

Properties of Dermis Skin

• Properties with fibers includes/involves connective tissue and vessels 2 mm thickness for the most parts in skin structure:
• collagen is elastic
• Vessels maintain blood
• Cells include fiber formation (collagin elastin).
• Appendix retains through hyaluronic in a mesoderm.

Subcutis and Tissue Structure

• Structure is mostly in adipocytes, tissue-based loose connective for cells and with fiber/fat areas, as with collagen/fat. It has large layers of tissues along with nervous supply.

Sense Organs: Mechanoreceptors and Chemoreceptors

• Functional sensory receptor is defined, including 5 functional types
• Free nerve mechano receptors explained with 3 encapsulated including:
• Pacinian corpuscles
• Meissner's corpuscles
• Ruffini's end organs
• Merkel's discs.
• muscle spindles
• Golgi tendon organs as proprioreceptors are defined.
• Structure of the taste bud chemoreceptors and their mechanism is recalled.
• The olfactory sense operation and membrane/function, is described.
• Sensory receptors include those for light touch, pressure, temperature, pain and the senses. These enable homeostasis

Major Senses Role

• Input into nervous system is receptors.
• Nerve endings/ cells that convert stimuli are signals in the external, internal. They're like, "afferent". Organs are auditory/optic for the information needed.
• the main senses provide part of sensory senses, but for general purposes, taste + body is important for senses.

Types of Functional & Sensory Receptors

• Categories classified into:
• Five functional categories

1. "Mechano" mechanical detections
2. "Thermo" temperatures change
3. "Nociceptors" free/tear pain
4. "Photo" retinal rods
5. "Chemo" smell

• Not always perfect classification.

Mechanoreceptors and Functions & Role

• Function most and nerve endings,
• Detect pain temperature through free cells/tissues.
• Nerve ending in skin muscles is surrounded

Tactile Receptors in Sensory Endings

• Types:
• Pacinian deep
• Meissner: Touch + vibration
• Merkel is lighting, and ruffini has tissue.

Pacinian Corpuscles Detailes

• Transmit via open
• Depolarize through pressure for signal, tissue detection is great with vibration. onion, 1 + meter is size.
• Found:
• abdominal
• external, tendons, and joints.

Ruffini Receptor Functions

• Tissue detect via nerve, for deformation in joints for the role/action of:
• pacinian through pressure
• thermo
• adapting is slow
• Capsule/Fiber with the "deeper".

Receptor Sizes and Characteristics

• Meissner's
• Has stacked lamellae.
• 75m long.
• It has the ability to detect touch that is light and for recognization. This is most acute at the lips, palms and face.
• Merkel has discs with epidermis (stratum) base, (light).
• Vesicles that are synapsed transmit without the neural (touch + small).
• Muscle for organ joints are Golgi/spindles. Adaptation, like for receptors, is slow.

Types of Response and Muscle Role

• Spindles are adaptation is slow and have no adaptation for continuous monitoring of tonic tone while being for position. The fibers can even be enclosed to impulses/sensory.

Muscle Fibers and Characteristics

• Muscles have attachment and immediate dendrite fibers, capsule/tendon.
• Spindles have a length and all have a fiber and signal and for sensory for control.

Adaptation Types and Nerves

• Rapid adaptation occurs between nerve stimulus is constant with the thalmic that has movement related.

Chemoreceptors Functions

• Taste and receptors
• Taste via organ with (3,000) that are 3,000 buds and arranged for 50/modified. roof in ororal, bud/ laryx.
• Two main types.

Types of Chemoreceptors

• Parts:
• epoglottis
• tonsils: lingual, etc.
• Regions: bitter, salty, sweet.
• Area bud responds: and is taste the is tested for that receptor but taste olfactory when have covid, cold, etc.

Taste Receptor Shapes

Sensation of Taste Types

• Hair type cells connect 50 or less near cell that taste.
• Sugar like G protein, can activate.

Gustatory Cells

Taste has cell types of base, gutaory long microvilli in brain

Taste Molecules and Cheminals

• The G protein interacts.
• This activates a protein kinase and closes K which opens Na+.
• High-Level: Ion is neuron and high.

Olfactory Sense/Function

• Epthelum can detect tetrapods smell, main sources of information are developed and the sensitive receptor can adapt.

Sensory Function of Small and Tissue

• The olfactory bulbs have sensors in cavity/tissue(wall) nose and Olfactory bulbs(tissue wall) in sinus.

Olfaction Mechanism and Properties

• Has membrane (contains the olfactory cells).
• Simple and
• Three cell types Bipolar: Support mucosa + ethmoid sensory bone.
• Fibers get through ethmoid .
• Mucosa: Can connect soma in the tissue where the project/cell in axons project (axon). Microvili + Epithelium with odor receptors. Then open channels (G), cause to enter and act. 7 scent classes. Very sensitive one per 30B.